Method for feeding electrical power into an electrical supply network

Abstract

A method for exchanging or feeding electric power into an electricity supply grid that has a grid frequency using a converter-controlled generator at a grid connection point is provided. The method includes feeding in electric power depending on a control function, where the electric power may comprise active and reactive power, and the control function controls the power depending on at least one state variable of the grid. It is possible to select between a normal control function and a support control function, different from the normal control function, as the control function. The normal control function is selected when it has been detected that the grid is operating stably and the support control function is selected when a grid problem, grid fault or an end of the grid fault has been detected. The support control function controls the fed-in power to counteract an oscillation in the grid.

The invention claimed is: 
     
       1. A method for feeding electric power into an electricity supply grid that has a grid frequency by way of a converter-controlled generator at a grid connection point, comprising:
 feeding in the electric power depending on a control function, wherein the electric power includes active power and reactive power, wherein the control function controls the electric power depending on at least one state variable of the electricity supply grid; 
 permitting selecting between a normal control function and a support control function, different from the normal control function, as the control function; 
 determining that the electricity supply grid is operating in a stable condition; 
 selecting the normal control function when it is determined that the electricity supply grid is operating in the stable condition; 
 detecting a grid problem, a grid fault or an end of the grid fault; 
 selecting the support control function when the grid problem, the grid fault or end of the grid fault is detected; wherein:
 the support control function controls the electric power to counteract an oscillation in the electricity supply grid, an oscillation of a synchronous generator connected to the electricity supply grid or an oscillation caused by the synchronous generator; 
 
 feeding the reactive power following the grid problem, grid fault or end of the grid fault; 
 using a reactive power function to feed in the reactive power, wherein the reactive power function specifies a relationship between a recorded voltage and the reactive power; 
 permitting selecting between a first and a second reactive power function as the reactive power function; 
 selecting the first reactive power function when it is determined the electricity supply grid is operating in the stable condition, or selecting the second reactive power function if a generator oscillation of the synchronous generator, associated with oscillation to the grid connection point, has been recorded, or if the generator oscillation is predicted; and 
 feeding the reactive power using a voltage-dependent reactive power support function, wherein the second reactive power function has a larger gain in terms of magnitude between the recorded voltage and the fed-in reactive power than the first reactive power function, wherein the normal control function includes the first reactive power function and the support control function includes the second reactive power function. 
 
     
     
       2. The method as claimed in  claim 1 , comprising:
 counteracting an oscillation caused by a response of the synchronous generator coupled directly to the electricity supply grid to the grid problem, the grid fault, or the end of the grid fault. 
 
     
     
       3. The method as claimed in  claim 1 , comprising:
 recording whether at least one synchronous generator associated with oscillation to the grid connection point is coupled to the electricity supply grid, wherein the synchronous generator associated with the oscillation to the grid connection point is arranged in a proximity of the grid connection point or acts to on the grid connection point, wherein a generator oscillation of the at least one the synchronous generator in which the at least one the synchronous generator oscillates in relation to an operating point or is measurable at the grid connection point as a frequency fluctuation or as a voltage fluctuation. 
 
     
     
       4. The method as claimed in  claim 1 , comprising:
 recording a frequency gradient in the electricity supply grid and at the grid connection point, and 
 following the grid problem, the grid fault or the end of the grid fault, resuming an active power infeed by the converter-controlled generator, and increasing the active power infeed with time, wherein increasing the active power infeed is performed in accordance with at least one rule from:
 increasing the active power infeed depending on the recorded frequency gradient, wherein the active power infeed is increased at a slower rate in the case of a positive frequency gradient than in the case of a negative frequency gradient, 
 increasing the active power infeed depending on the recorded frequency gradient such that a rate of the increase is decelerated with an increasing frequency gradient, and is accelerated with a decreasing frequency gradient, and 
 increasing the active power infeed depending on a peak value of an oscillating frequency gradient such that, when the peak value is reduced with decelerating frequency oscillation, the rate of the increase in the active power infeed is increased. 
 
 
     
     
       5. The method as claimed in  claim 1 , comprising:
 recording a frequency value of the grid frequency in the electricity supply grid and at the grid connection point, and 
 following the grid problem, grid fault or end of the grid fault,
 resuming an active power infeed by the converter-controlled generator, and 
 increasing the active power infeed with a rate of increase, wherein the rate of increase depends on a peak value of the grid frequency, wherein the peak value decreases as frequency oscillation decreases, and wherein when the peak value decreases, the rate of increase of the active power infeed increases. 
 
 
     
     
       6. The method as claimed in  claim 1 , wherein
 the support control function implements a behavior of a virtual synchronous machine with a rotor inertia having a predefined moment of inertia, 
 the behavior of the virtual synchronous machine is implemented at least such that:
 a change in the grid frequency results in a change in active power and the change in the fed-in active power is positively correlated with the predefined moment of inertia, or 
 a fed-in infeed current lags or leads a grid voltage when the grid frequency changes, and the lag or lead is positively correlated with the predefined moment of inertia. 
 
 
     
     
       7. The method as claimed in  claim 6 , comprising:
 activating the behavior of the virtual synchronous machine or increasing the moment of inertia following the grid problem, grid fault or end of the grid fault, or 
 activating the behavior of the virtual synchronous machine or increasing the moment of inertia if oscillation of the grid frequency is detected, when the oscillating frequency passes through a pre-fault grid frequency that was recorded before the grid problem or grid fault occurred. 
 
     
     
       8. The method as claimed in  claim 1 , comprising:
 implementing damping control for active oscillation damping in the support control function, or 
 to feed in electric power, modulating a fed-in or drawn reactive power by modulating the converter-controlled generator as an admittance. 
 
     
     
       9. The method as claimed in  claim 8 , wherein the damping control includes at least one function from:
 a simulation or emulation of a frequency-dependent load; and 
 a simulation or emulation of a voltage-dependent load. 
 
     
     
       10. The method as claimed in  claim 1 , comprising:
 selecting or parameterizing the support control function depending on a converter saturation, wherein the converter saturation is a measure of a proportion of power fed in by converter-controlled generators into the electricity supply grid to an overall power fed into the electricity supply grid. 
 
     
     
       11. The method as claimed in  claim 10 , wherein the overall power includes power fed in by synchronous machines coupled directly to the electricity supply grid. 
     
     
       12. The method as claimed in  claim 1 , wherein the support control function includes performing damping, and the normal control function does not include performing the damping. 
     
     
       13. The method as claimed in  claim 12 , wherein the support control function includes performing damping, and the normal control function does not include performing the damping. 
     
     
       14. The method as claimed in  claim 1 , wherein:
 when an oscillation of at least one synchronous machine is recorded in the electricity supply grid, a rapid active power recovery is performed. 
 
     
     
       15. The method as claimed in  claim 14 , wherein a converter proportion is a measure of power fed in by converter-controlled generators into the electricity supply grid to an overall power fed into the electricity supply grid, and wherein in response to the converter proportion being at least 90%, the rapid active power recovery is a faster active power recovery than predefined by the support control function. 
     
     
       16. A converter-controlled generator for feeding electric power into an electricity supply grid that has a grid frequency, comprising:
 an infeed apparatus configured to feed in the electric power depending on a control function, wherein the electric power includes active power and reactive power; and 
 a controller configured to:
 implement the control function, wherein the control function controls the electric power depending on at least one state variable of the electricity supply grid; 
 permit selection between a normal control function and a support control function, different from the normal control function, as the control function; 
 select the normal control function when it is determined that the electricity supply grid is operating in a stable condition, and select the support control function when a grid problem, grid fault or an end of the grid fault has been determined recognized, wherein the support control function controls the electric power to counteract an oscillation in the electricity supply grid, an oscillation of a synchronous generator connected to the electricity supply grid or an oscillation caused by the synchronous generator; 
 cause the reactive power to be fed following the grid problem, grid fault or end of the grid fault; 
 use a reactive power function for causing the reactive power to be fed, wherein the reactive power function specifies a relationship between a recorded voltage and the reactive power; 
 select between a first and a second reactive power function as the reactive power function; 
 select the first reactive power function when it is determined the electricity supply grid is operating in the stable condition, or select the second reactive power function if a generator oscillation of the synchronous generator, associated with oscillation to a grid connection point, has been recorded, or if the generator oscillation is predicted; and 
 cause the reactive power to be fed using a voltage-dependent reactive power support function, wherein the second reactive power function has a larger gain in terms of magnitude between the recorded voltage and the fed-in reactive power than the first reactive power function, wherein the normal control function includes the first reactive power function and the support control function includes the second reactive power function. 
 
 
     
     
       17. The converter-controlled generator as claimed in  claim 16 , wherein the converter-controlled generator is a wind power installation. 
     
     
       18. A wind farm having a plurality of wind power installations including the wind power installation as claimed in  claim 17 , comprising:
 a farm controller configured to generate power setpoint values and transmit the power setpoint values to the plurality of wind power installations. 
 
     
     
       19. A method for feeding electric power into an electricity supply grid that has a grid frequency by way of a converter-controlled generator at a grid connection point, comprising:
 feeding in the electric power depending on a control function, wherein the electric power includes active power and reactive power, wherein the control function controls the electric power depending on at least one state variable of the electricity supply grid; 
 permitting selecting between a normal control function and a support control function, different from the normal control function, as the control function; 
 determining that the electricity supply grid is operating in a stable condition; 
 selecting the normal control function when it is determined that the electricity supply grid is operating in the stable condition; 
 detecting a grid problem, a grid fault or an end of the grid fault; 
 selecting the support control function when the grid problem, the grid fault or end of the grid fault is detected; wherein:
 the support control function controls the electric power to counteract an oscillation in the electricity supply grid, an oscillation of a synchronous generator connected to the electricity supply grid or an oscillation caused by the synchronous generator; and 
 
 selecting or parameterizing the support control function depending on a converter saturation, wherein the converter saturation is a measure of a proportion of power fed in by converter-controlled generators into the electricity supply grid to an overall power fed into the electricity supply grid.